1. Field of the Invention
The present invention relates to a vehicular brake control apparatus exhibiting a high braking force, and more particularly, to a brake control apparatus which can provide, to wheel cylinders, a brake-fluid pressure higher than master-cylinder pressure generated by a master cylinder, in a case where obtaining higher braking force is desirable on a road having a high friction coefficient or the like.
2. Related Arts
U.S. Pat. No. 5,427,442 discloses a brake fluid pressure boosting apparatus for an automobile which boosts brake-fluid pressure applied to wheel cylinders to obtain optimal braking force. In the brake fluid pressure boosting apparatus, a boosting effect due to a brake-pressure booster is intensified in a state of panic braking wherein a driver hesitates to depress a brake pedal with maximum force. As a result, wheel-cylinder pressure larger than normal in response to a driver's pedal-depression force is applied to the wheel cylinders and a high braking force is secured.
The prior art apparatus, however, increases wheel-cylinder pressure by intensifying the boosting effect only in a case where a pedal-depression force increase gradient is higher than a predetermined increase gradient.
Further, U.S. Pat. No. 5,350,225 discloses a braking force amplifying apparatus which amplifies a braking force when a moving speed of a brake pedal caused by a driver's depressing operation exceeds a predetermined threshold value. This apparatus, however, is not effective enough in all cases either. For example, when a driver further depresses the brake pedal from a state that the brake pedal has been depressed to some extent, because the brake pedal can not move over a long distance, a moving speed of the brake pedal does not become high enough to exceed the predetermined threshold value. Therefore, even if the apparatus has the structure that can realize higher wheel-cylinder pressure, the desirable high braking force can not always be obtained.